Skin testing for allergy has conventionally been performed by putting a small drop of the suspected allergen on the back or the forearm of the subject and then exposing the underlying tissue by pricking the skin with a needle. An inflammatory response occurring within about 10-15 minutes indicates allergy to the suspected substance. Commonly, allergy to between 5 and 20 suspected substances may be tested in this way at any one time. This test commonly called the "skin-prick test", has remained essentially unchanged in its design since it was first introduced over 70 years ago. The method, still widely used by specialists in the field of allergic disease, is not as popular with general practitioners since it takes up valuable consultation time in the surgery, is uncomfortable for the subject and is costly to provide, especially if it is only done occasionally. Prick testing also requires some technical skill and is quite labour intensive. However, it is the most reliable method of those used to diagnose allergy and gives a result within 10 to 30 minutes of starting the test.
In a similar manner, testing for cell-mediated immunity may be performed by either injecting a small quantity of antigen under the surface of the skin using a needle and syringe or by puncturing the skin and allowing antigen solution to passively infiltrate the puncture site. The skin reaction, which is an index of the patient's ability to mount an immune response to the test antigen, is usually measured many hours to several days later.
In the last 15 years, an alternative method of testing for allergy using an in vitro assay has been introduced. The assay requires the use of serum, the reagents used are costly, assays are only performed by specialist pathology laboratories, and several days may elapse before a result is known. Because of the cost, the number of tests which can be performed is often limited to 4 suspected allergens. Only in rare circumstances do such in vitro assays offer any advantages over skin tests, for example where the skin of a patient with eczema is highly inflamed, or when the patient is taking a particular drug which interferes with the skin test response. The correlation between results from skin prick tests and in vitro tests is only about 70% and there are several reasons why such in vitro tests sometimes produce false negative and false positive reactions. Despite this, these assays are very popular (well over 100 million have been performed internationally), and despite several more companies entering the field recently and the introduction of minor changes in design and/or procedure, no major improvements have been made.
It would be desirable to adapt the skin test to make it more available and acceptable to both patient and physician, and to improve the speed and reliability of the diagnosis of immune-mediated responses. Reduction of the costs of both tests would also, of course, be welcome.
An object of the present invention is to refine the existing methods of skin testing for the diagnosis of both immediate and delayed immune reactions. The procedure when the device of the present invention is employed does not require any specialized technical expertise and is sufficiently simple to be used, without specialised training, by general practitioners (GPs). It is also more acceptable to patients than when conducted according to prior art techniques.